Welp ... that was easy.
I rinsed a 1.75 gal torpedo keg with water, and the dual-reg setup for the BeerGun happens to be perfect for flushing and quick carbonating ...
I put the end of the tube that normally screws onto the 1/4" MFL for the BeerGun into the bottom of the keg, flushed it out for 10 seconds, and then poured the beer from the LBMB into the keg as quickly and gently as possible, popped the lid on the keg, and flushed the head space, and finally set the pressure to 35 psi ...
It took me 2 minutes to clean the fermenter, since the mouth of the LBMB is massive ...